This invention relates to a method of utilizing ultrasonic welding technology to splice together photographic film strips, and especially motion picture films having dissimilar polymeric supports. In particular, the invention relates to process conditions that can be employed with currently available commercial ultrasonic splicing devices designed for splicing polyester based films that will allow successful splicing of acetate support (e.g., cellulose triacetate (CTA)) based films to themselves and especially splicing of acetate based films to polyester support (e.g., polyethylene terephthalate (PET)) based films.
Motion picture photographic films used in producing a release print (the film projected in movie theaters) include camera origination film, intermediate film, and the release print film. Current practice for most motion picture film production involves the use of at least four photographic steps. The first step is the recording of the scene onto a camera negative photographic film. While the original negative (typically after editing) may be printed directly onto a negative working print film in a second step to produce a direct release print, most motion picture productions use an additional two intermediate steps. Typically, the original camera negative film is printed onto a negative working intermediate film, such as Eastman Color Intermediate Film, yielding a master positive. The master positive is subsequently printed again onto an intermediate film providing a duplicate negative. Finally, the duplicate negative is printed onto a print film forming the release print. In practice, several duplicate negative copies are produced from the master positive, and each of the duplicate negatives may then be used to make hundreds of print film copies. This multistep process helps save the integrity of the valuable original camera negative film in preparing multiple release prints. In certain situations, usually involving special effects, intermediate film may be used an additional two or more times in preparing the final duplicate negatives to be used in printing the release prints. In this case, the first duplicate negative is used to print onto intermediate film to produce a second master positive, which is in turn used to produce a second duplicate negative. The second duplicate negative may be then used for printing the release prints.
The wide variety of potential film products available for the above mentioned processes can be produced on either of two commonly employed polymeric supports: cellulose triacetate (CTA) and polyethylene terephthalate (PET). It is becoming more common for specific film codes to be available on only one of these supports as opposed to either. Historically, acetate-based films, and the older, less common cellulose nitrate-based films, were spliced to themselves using film cement comprising organic solvents designed to partially solubilize the cellulose-based film supports. Satisfactory cement splicing requires careful scraping away of the emulsion layers of the lower film component prior to application of the film cement in order to allow intimate support contact. It is also important to allow sufficient clamping time in the splicer. Current recommendations are fifteen to thirty seconds under modest heat and pressure prior to handling of the splice. Because a cement splice does not attain full strength for several hours, care is required when handling the film if immediate use is contemplated. Not only is this splicing technique cumbersome, time consuming, and a source of debris, but there are also health, safety and environmental concerns surrounding the components of the currently employed film cements.
With the advent of PET-based film products, a new splicing technique was required since this film support does not readily lend itself to cement splicing. The polymer used as the support base is not soluble in the solvents used in film cement and even more toxic solvents would be required to produce the same type of bonding with PET-based films. The most common method of splicing PET-based film, when it was originally introduced, was the use of pressure sensitive tapes. These tapes are costly, cumbersome, and require application to imaged frames adjacent to the splice itself.
A more convenient method of splicing PET-based films has been with the use of ultrasonic energy to essentially xe2x80x9cweldxe2x80x9d the two film members together. This splicing technique is typically accomplished in an overlap configuration, and within an area that will exclude perforations and/or an imaged frame. U.S. Pat. Nos. 3,574,037 and 4,029,538, and EP 0497 393, e.g., describe systems and apparatus employing the use of ultrasonic sealing devices that can be used to splice films, specifically motion picture films. These patents, however, refer only to the splicing or welding of polyester-based film products. In addition, U.S. Pat. Nos. 5,356,682 A1 and 5,447,588 A1 teach the use of ultrasonic splicing of polyester (PET) webs used in the manufacture of photographic film support. Other patents, most notably U.S. Pat. Nos. 5,679,207 A1 and 5,961,025 A1, teach the use of ultrasonic energy and the developed apparatus that can be used to prepare lap splices on unspecified polymeric supports that could be used in the manufacture of photographic film base.
While the use of ultrasonic welding techniques have been suggested for splicing of acetate based film strips, attempts to do so have generally not been successful. Motion picture film splicers that have been developed which utilize ultrasonic energy to splice PET-based films together, e.g., when used to splice CTA-based films, cause brittleness and diminished strength typically resulting in splices which are far too weak and/or rough for practical application. Such splices also may exhibit levels of roughness that are likely to damage adjacent areas of film when wound in roll form. Additionally, the increased thickness produced by the molten acetate material may prevent splices from smooth conveyance through the tight tolerances encountered in film printing gates. Similarly, using existing ultrasonic splicing devices to join CTA and PET film stocks produces the same rough, distorted surface of the acetate film member. U.S. Pat. No. 3,700,532, e.g., notes some typical problems associated with attempts to ultrasonically splice acetate based film strips together.
There are numerous other patents that utilize similar ultrasonic technology and sealing equipment but are not related to the splicing of motion picture film or other photographic applications. One such example is U.S. Pat. No. 4,490,199 A1, which relates to a method and apparatus for splicing polymeric webs using a xe2x80x9cspot weldingxe2x80x9d technique that employs ultrasonic energy as a means creating the splice. The polymeric webs cited in the example consist of a filled polycaprolactam composite. U.S. Pat. Nos. 3,728,183 A1 and 3,904,474 A1 also deal with the use of ultrasonic splicing thermoplastic sheets in non-photographic applications.
Another example is U.S. Pat. No. 5,632,831 A1, which relates to the use of an ultrasonic sealing device that can be used to splice together (unspecified) polymeric webs. More specifically this patent pertains to the removal of defective areas and re-joining the web in a seamless manner as a quality control improvement in the manufacture of consumer product packaging materials.
Current commercially available ultrasonic splicers for photographic film strips, and in particular motion picture film strips, include those manufactured by the Hollywood Film Company and the Metric Splicer and Film Company, Inc. Both manufacturers produce splicing units that will adequately fuse polyester film to itself (either raw or processed) without the need for tape, solvent cement, or emulsion scraping. Each manufacturer provides splicing units which utilize an elongated ultrasonic horn that is approx. 2 mm in width and 38 mm in length, mounted in the base of the units. The film members intended to be spliced together are mounted such that overlapped ends of each film member positioned are above this horn, with the length of the horn extending across the width of the film strips. During use, the horn is energized, and intimate contact is then made between the horn and the film strips as an anvil positioned on the opposite side of the film strips (relative to the horn) traverses over the film members in the length direction of the horn such that ultrasonic energy from the horn is transferred to the overlapping film ends effecting an ultrasonic weld between such film ends.
One notable difference between different commercial units is the design and geometry of the anvil. The Hollywood Film Company HFC 2K model utilizes a radiused, polished steel sled-type anvil having a width of 4 mm and a length of 10 mm. This sled is pulled across the film members using a cable and pulley system. As supplied by the manufacturer, the model HFC 2K splicer is provided with an anvil pressure of approximately 1.8 kg and an anvil traverse time of eight seconds across a 35 mm film strip (traverse rate of approx. 4.4 mm/sec).
The Hollywood Film Company HFC 24700 model and the Metric Splicer and Film Company, Inc. Model 3001 ultrasonic film splicers both utilize a polished steel roller having a width of 6 mm and a diameter of 20 mm, which is rolled across the overlapped film members. The HFC 24700 model unit uses a cable and pulley drive whereas the Metric Model 3001 unit uses a rack and pinion drive mechanism. As supplied by the manufacturer, Hollywood Film Company""s model 24700 splicer has an anvil pressure of approximately 0.9 kg and an anvil traverse time of eight seconds across a 35 mm film strip (traverse rate of approx. 4.4 mm/sec). As supplied by the manufacturer, The Metric Model 3001 splicer has an anvil pressure of approximately 1.0 kg and an anvil traverse time of 7.5 seconds across a 35 mm film strip (traverse rate of approx. 4.7 mm/sec).
While the above described commercially available ultrasonic film splicers are effective for splicing polyester based film strips to each other, to date no one has provided a method for successfully splicing together motion picture film strips composed of dissimilar polymeric supports (and in particular, the splicing of acetate based films to polyester based films) that does not rely on the use of pressure-sensitive tape. The prior art has also failed to provide a method of splicing cellulosic-based motion picture film without the need for removal of the emulsion layer and application of a flammable and toxic solvent mixture. It would be particularly advantageous to provide a method for using the commercially available types of ultrasonic splicers employing sliding or rolling anvils for splicing acetate based film strips to each other, and especially for splicing acetate based film strips to polyester based film strips.
In accordance with one embodiment of the invention, a method is described for ultrasonically splicing together overlapping ends of first and second lengths of photographic film strips of common film strip width with a film splicer employing a stationary elongated ultrasonic horn positioned on one side of the overlapping film strip ends in the width direction and a relatively movable anvil positioned on the opposite side of the overlapping film strip ends which traverses across the overlapping film ends by sliding or rolling in the length direction of the horn while the horn is ultrasonically vibrated and which provides pressure to the overlapping film ends while traversing across the overlapping film ends such that ultrasonic energy from the horn is transferred to the overlapping film ends effecting an ultrasonic weld between such film ends, wherein one of the first and second lengths of photographic film strips comprises an acetate based film strip and the other of the first and second lengths of photographic film strips comprises an acetate based film strip or a polyester based film strip, and wherein the product of the anvil pressure and anvil traverse rate is less than 6.0 kg.mm/sec when the anvil is slid across the overlapping film ends and less than 3.5 kg.mm/sec when the anvil is rolled across the overlapping film ends.
The method of the invention enables the use of existing commercially available ultrasonic splicers to splice either polyester-based films to acetate-based films or acetate-based films to themselves and provide an adequate level of splice strength and smoothness. The invention enables formation of composite rolls of motion picture film containing different film bases as well as eliminating the need for emulsion skiving, and the use of toxic, flammable film cements when splicing CTA films.
In a preferred embodiment, anvil pressure and anvil traverse rates are specified that will allow successful splicing of acetate-based film to itself or to PET-based films using an ultrasonic splicer employing a sliding anvil such as Model HFC 2K ultrasonic film splicer from Hollywood Film Company.
In another embodiment, anvil pressure and traverse rates are specified that will allow successful splicing of acetate-based film to itself or to PET-based films using an ultrasonic splicer employing a rolling anvil such as a Model 24700 ultrasonic film splicer from Hollywood Film Company or a Model 3001 ultrasonic film splicer from Metric Splicer and Film Company, Inc.